The present invention relates to stabilized sighting apparatus and is particularly but not exclusively suitable for use in fire control systems located on movable platforms, particularly land vehicles, helicopters and boats. There exist fire control systems designed to maintain the elevation and azimuth angles of the lines of sight of several units operating in different wavelength fields, such as a direct observation sighting telescope, a TV camera working in the visible or near infrared portion of the electromagnetic spectrum, a deviation detecting device, a thermal-imaging apparatus. The lack of material having a satisfactory transmission coefficient in the whole of the useful spectrum, from visible light to thermal infrared, has frequently led to use of at least two separate apparatuses to cover the whole of the spectrum, one being typically provided for the 0.4 to 2.5 micron field and the other for the 4 to 14 microns field.
It is an object of the invention to provide a multi-wave sighting apparatus, which is of acceptable overall size and reduced in weight and whose aiming stability is comparable to those of prior apparatuses.
According to the invention, there is provided a stabilized sighting apparatus comprising a structure mounted for rotation about a first axis on an assembly mounted for rotation about a second axis orthogonal to the first on a platform, a thermal infra-red camera carried by the structure, inertial means carried by said structure for controlling drive means associated with the structure and assembly for stabilization about the two axes, optical sight means having an aiming mirror mounted on said assembly for rotation about an axis parallel to said first axis, drive means drivably connected to said mirror for impressing angular movements to said mirror reproducing the movements of the camera, and optical means for transferring a light beam received from the mirror toward the platform at a location close to the second axis, said infrared camera being so located as to be traversed by the second axis and the larger portion thereof being opposite the mirror in relation to said second axis.
The inertial system is advantageously fast with an elevation ring supporting directly the camera for maximum stability.
An harmonizing collimator and associated reflectors directing light towards the camera and towards the mirror may be connected to the elevation ring; with such a system, it is possible to measure a possible angle between the lines of sight of the different detection units in relation to each other, at any moment and whatever the aiming angles. The harmonizing system connected to the supporting structure of the gyroscope and therefore stabilized may additionally be associated with an electronic circuit which delivers data representative of dynamic structural deformation if any; such deformation may then be taken into account so as to improve the stabilizing performances.
If the collimator is only used for harmonizing, reflectors may be provided with means for retracting them by rotation in order to avoid constant occultation of the pupils of the associated optical elements, such as the TV camera and the aiming mirror.
By substituting a recopying device with a ratio 1/2 for the stabilizing system usually provided for the aiming mirror, the weight, bulk and cost of the assembly is substantially reduced. This is without attendant disadvantage when the visible image is directly observed by an operator since the required aiming stability is smaller than in the case where a camera is used, given the possibilities of adaptation and of interpretation of the human eye.
The assembly rotatable about the second axis may be formed by an azimuth ring which supports, in addition to the aiming mirror, a Galilean telescope with variable magnification and a dichroic separator. On leaving the separator, the visible part of the light spectrum is reflected by optical displacement means to be directed along the second axis whereas the infra red portion is sent towards a rangefinding system also supported by the azimuth ring.
Such an arrangement presents numerous advantages: by placing the Galilean telescope directly behind the mirror, the size of the mirror and of the transparent window for the visible portion of the spectrum may be reduced and consequently the size of the apparatus.
The invention will be better understood from the following description of a particular embodiment thereof, given by way of example. The description refers to the accompanying drawings.